refac: mermaid chart rendering

src/lib/components/chat/Messages/CodeBlock.svelte

@@ -222,6 +222,9 @@ __builtins__.input = input`);
 </script>
 
 <div class="my-2" dir="ltr">
+	{#if lang === 'mermaid'}
+		<pre class="mermaid">{code}</pre>
+	{:else}
 		<div
 			class="flex justify-between bg-[#202123] text-white text-xs px-4 pt-1 pb-0.5 rounded-t-lg overflow-x-auto"
 		>
@@ -273,4 +276,5 @@ __builtins__.input = input`);
 				<div class="text-sm">{stdout || stderr || result}</div>
 			</div>
 		{/if}
+	{/if}
 </div>